An example of a card connector which uses a single circuit board for signal and ground connections between cards and a mother board is disclosed in Japanese Patent Application No. 9-22762. The card connector has card accommodating sections arranged in two stages, i.e., an upper stage card-accommodating section and a lower stage card-accommodating section. A circuit board is disposed along a back surface of the card connector, and it is used for mutual connections at a relatively high frequency. The circuit board contains four layers of circuit wiring; the inner two layers are used for signal lines, while the outer two layers are used for ground lines. However, a manufacturing process for making a four-layer circuit board is relatively complicated, and the manufacturing cost is also high. Accordingly, an important object of the present invention is to provide a card connector circuit board which is easy to manufacture, and which can provide good electrical characteristics with respect to the signal and ground lines.